Secondary batteries which are highly applicable to various products and exhibit superior electrical properties such as high energy density, etc. are commonly used not only in portable devices but also in electric vehicles (EVs) or hybrid electric vehicles (HEVs) driven by electrical power sources. The secondary battery is drawing attentions as a new energy source for enhancing environment friendliness and energy efficiency in that the use of fossil fuels can be reduced greatly and no byproduct is generated during energy consumption.
Secondary batteries widely used at the preset include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries and the like. An operating voltage of the unit secondary battery cell, namely a unit battery cell, is about 2.5V to 4.2V. Therefore, if a higher output voltage is required, a plurality of battery cells may be connected in series to configure a battery pack. In addition, depending on the charge/discharge capacity required for the battery pack, a plurality of battery cells may be connected in parallel to configure a battery pack. Thus, the number of battery cells included in the battery pack may be variously set according to the required output voltage or the demanded charge/discharge capacity.
Meanwhile, when a plurality of battery cells are connected in series or in parallel to configure a battery pack, it is common to configure a battery module composed of at least one battery cell first, and then configure a battery pack by using at least one battery module and adding other components.
A conventional battery module generally includes a plurality of battery cells and a module case that accommodates the plurality of battery cells. In addition, the module case includes a case body and a plurality of cell cartridges provided inside the case body to accommodate at least one battery cell. In the conventional battery module, electrode leads of two battery cells facing each other and accommodated in the module case may be welded and electrically connected to each other through a lead welding apparatus at the outside of the module case.
For this, a conventional lead welding apparatus includes a welding unit for welding two electrode leads arranged to overlap each other at the outside of the module case by laser welding, and a welding jig for pressing one side and the other side of two electrode leads of the battery cells facing each other when the welding is performed so that two electrode leads overlap each other.
However, in the conventional battery module, when the electrode leads are welded, the welding jig of the lead welding apparatus presses the two electrode leads to be closely adhered to each other at one side and the other side of the two electrode leads. When the pressing is performed, due to a pressing force transferred at both sides of the two electrode leads, the force is transmitted to the case body and the cell cartridges of the module case more than necessary, which may bend or damage the case body and the cell cartridges.
In addition, in the conventional battery module, if the module case is damaged, when the welding unit injects laser or the like for welding, the deviation of a focal distance of the welding unit may be influenced, which may deteriorate welding quality. Moreover, a welding defect between the electrode leads caused by the deterioration of welding quality may increase contact resistance later, which may cause heat generation of the battery module. In addition, when external vibration or impact occurs, the connection between the welded electrode leads may be easily broken.
Therefore, in order to solve the above problems, it is required to find a way to prevent the module case from being damaged when the electrode leads of the battery cells of the battery module are welded and to improve the welding quality.